Field devices for industrial processes generally signify regulating devices, control devices, sensors, transducers, and the like, directly connected to the process. A typical field device is a control valve provided with a valve controller, such as the valve controller ND800 of Neles Controls Oy. So-called intelligent field devices are provided with a control logic and software, which make it possible to control the field device locally for instance by means of a suitable control algorithm, to collect status and measurement data and/or to communicate with an automation system or a field device management system.
FIG. 1 illustrates a general diagram of a process automation system and an associated maintenance management system of field devices. The automation system comprises control room programs and databases 11 as well as process control programs and an I/O part 12. Traditionally, the field devices have been connected to the control system by two-wired twisted pair loops, each device being connected to the control system by a single twisted pair providing a 4–20 mA analog input signal. More recently, new solutions, such as Highway Addressable Remote Transducers (HART) protocol, that allow to transmit digital data together with conventional 4 to 20 mA analog signal in the twisted pair loop, have been used in the control systems. In the most recent phase of evolution, a field control system (FCS) has been introduced which employs a totally digital high-speed network or data bus for interconnecting the control room computer and the field devices. The analog switched pair loops are omitted in the FCS. A new communication protocol is generally referred to as fieldbus have been defined by the Instrument Society of America (ISA). With reference to the architecture illustrated in FIG. 1, the control and I/O part 12 is connected via HART buses to intelligent field devices, such as control valves 14, 15, 16 and valve controllers 14A, 15A, 16A. HART enables a two-way communication, by means of which the intelligent field devices can be controlled, configured and monitored. The HART protocol is described in greater detail for instance in the publication HART field communication protocol: An introduction for users and manufacturers, HART Communication Foundation, 1995. Again with reference to FIG. 1, field devices are monitored by a field device management system 10 which collects data from the field devices. For this purpose, each field device 14, 15 and 16 is connected via respective field bus to a conventional HART multiplexer 9, which again is connected via an RS-485 bus 8 to a PC 6. It should be appreciated that the architecture shown in FIG. 1 is only one example of possible control and management system architectures. For example, the field device management system may be partially or totally integrated into the automation system. However, as the field devices are typically supplied by different manufacturers than the automation system, the diagnostics of the field device is normally an area belonging to the field device supplier and not to the supplier of the actual automation system, and therefore, very often separate management systems are provided.
Therefore, at least in some automation and field device management systems intelligent field devices can be configured, controlled, and/or monitored by the operator of the plant from the control room. However, it is desired that also the maintenance personnel in different locations in the plant are capable of monitoring, configuring and controlling the field devices. A prior art approach is to provide the maintenance personal with special purpose communicator for configuration of the field devices, such as a hand-held HART communicator which can be connected to the HART bus via special purpose configuration ports.
Another approach is disclosed in U.S. Pat. No. 5,793,693, wherein each field device is provided with a wireless field bus port that is accessible by wireless hand-held unit or wireless terminal in order to obtain non-redundant secondary access to a field device that is controlled by a control room. This approach avoids the need for physical connection to the field bus or the field device but still requires a special-purpose communicator and a dedicated control software for each different type of field devices.
A still another approach is a GSM-control concept provided by Klinkmann, Finland. GSM control is a PC (Personal Computer) software which allows to use standard low-cost GSM cellular phones as two-way remote controllers. A GSM modem is connected to the PC by a RS232 serial port. The communication between the GSM phone and the GSM modem is a standard SMS (Short-Message-Service) communication via a public GSM network which enables a transfer of text messages between the GSM phone and the GSM control program running in the PC. The GSM control software can be connected to other windows programs and software. This GSM control approach might be suitable also for controlling and managing field devices in an industrial process. The benefit would be that standard cellular phones can be used instead of special purpose diagnostic terminals. However, the communication based on SMS messages transmitted via a public GSM network is not reliable enough for controlling industrial processes. The transfer times of the short messages may vary from seconds to hours, and the messages may even be lost without ever reaching the recipient, due to the traffic load variation in the SMS centres and the GSM network involved. This results in intolerable response times from inputting a control command by the maintenance person at the cellular phone until the command is received and performed by the automation system or the field device. The maintenance person cannot even be sure whether the message is received or not. Therefore, the user of the standard SMS concept of the GSM system is not suitable for control and configuration of field devices in an industrial process.
A further problem relating to the known GSM control concept is a complicated management of various interrelated data, such as users, phone numbers, passwords, DDE addresses, read messages, write messages, alarm/event messages, default messages, etc. According to a current specification this data is linked with each other according to the following hierarchy: at the highest level there are configured users, each user being able to have several phone numbers and passwords. For each passwords there are pointers to corresponding read, write, alarm/event or text messages. These messages are further linked with appropriate DDE addresses. In an industrial process there may be hundreds of field devices, and therefore it will be in practice impossible for a maintenance person to cope with this information and to easily and efficiently make the control procedures. Further, it is difficult to maintain the information updated.